1. Field of Invention
The present invention relates to the packaging of electronic assemblies. More particularly, it is directed to a spring grounding clip and its combination with a computer peripheral or memory card.
2. Description of Related Art
Electronic assemblies are useful in a wide variety of electronic systems for ease of configuration of specific capabilities of such a system. One such type of assembly includes interface devices which plug into either a serial or parallel port of a personal computer (PCs), such as security keys, video adapters, and LAN interfaces. Another such type of assembly are peripheral cards for personal computers. Until recently, most card were unprotected circuit boards, having edge connectors and carrying a variety of circuit components soldered thereto, and which cards were installed into a PC by opening the case of the PC and inserting the card's edge connector into a mating backplane connector.
Recently, a new type of PC peripheral card standard was adopted by the industry known as the PCMCIA card. Even though originally developed for memory expansion cards (the acronym "PCMCIA" stands for "Personal Computer Memory Card International Association"), this standard has since seen wide adoption in a wide variety of peripheral cards, such as RAM (volatile memory), FLASH EEPROM (non-volatile memory), hard disks, FAX/modems, data acquisition interfaces, and LAN interfaces, and has become virtually standard fare for recently introduced laptop, sub-laptop, and personal digital assistant (PDAs) computers. PCMCIA Interfaces are also available for more traditional desktop computers, as well.
PCMCIA cards are very popular because of their small size, standardized interface, standardized form factor, ease of end-user installation, and lower risk of end-user caused damage to a host electronic system. Nonetheless, cost is still a major issue, and lower cost is still desired. Due to the extremely small size of a PCMCIA card, packaging costs are potentially higher than larger format packaging solutions. Assembling a PCMCIA card typically requires high precision, surface-mount, printed wiring board (PWB) manufacturing techniques.
A typical PCMCIA card or other type peripheral card including a memory card hereafter collectively called a "peripheral card" includes a printed wiring board (PWB) and attached circuit components including a board connector, various surface-mounted integrated circuit chips, other electronic components and plated electrical traces extending between such components. In some applications, such as data encryption or decryption, a battery source of power and various electronic components maybe contained on either or both sides of the peripheral card as well as components with plated vias extending through the PWB. A two-part overlying protective metal-plastic cover has been employed where the peripheral card is clamped between the two parts of the cover with the peripheral card cantilevered from a connector end edge of the peripheral card and held in place by abutting clamped edges of the cover parts. The desirability of dissipating any electrical static charge on the metal cover as well as a need to provide a means to ground the conductive case for the purpose of shielding the card from radiating or receiving electro-magnetic interference (EMI) has been recognized. Others have used separate C-shaped spring clips available from Molex, Inc. of Springfield, Ill. or Z-shaped spring clip available from Duel Systems, Inc. of San Jose, Calif., each extending from opposite sides of the PWB to a facing metal cover part to both space the PWB from the cover inner surfaces and provide an electrical ground path from the metal of the cover part to the ground circuit of the printed circuit board. The C-clips or Z-clips have a height such that the height of electronic components on the PWB are accommodated and the components do not contact the metal covers. While the C- and Z-clips when compressed by the cover plates do have some wiping action such wiping tends to cause the clips to be forced off away from the conductive pad on the surface of the PWB edge. In still another system, namely in a HP 512 RAM memory card, coil springs are positioned in PWB insulative bores. The coils extend from opposite sides of the PWB toward the cover parts and are adapted to be compressed between the cover parts. This acts to space the PWB when the cover parts are clamped together and subsequently joined together such as by pressure sensitive adhesive foam. In this system, a special housing and special tooling is needed to accommodate an additional clip which electrically contacts the cover through the coil springs.
In the event the PWB is to be offset between the protective covers due to the greater height of components on one side of the PWB, it is necessary that two different sizes of C-clip or Z-clips be employed to accommodate the different heights. Further, if the components are all on one side of the PWB, it would still be necessary to flip the PWB over to put a spring contact pad on the PWB underside on which the underside clip would abut and via a plated via conduct a static charge to a trace and ground socket or pin on the component-containing side of the PWB. This also adds process steps and needs additional tooling, both of which adds to production costs. Use of different sizes of clips also increases tooling and process cost. If one were to use an intermediate size to accommodate the different spacings too little force would be put on the PWB on one side and too much force would be put on the opposite side of the PWB.
The four C- or Z-clips which are used in the prior art result in different forces on the PWB due to different compression of the clips by the cover parts due to the PWB offset. These unequal forces tend to force the clips off of the PWB surface grounding pads and cause the board to impart stress to the laminated board and plated copper traces. The grounding clips of the above related art all tend to be compressed against the contact pads on the PWB which compression also compresses any contaminant such as oils or oxides on the surface of the contact area.
From the above, there has been a need of a grounding clip which can balance the forces on the PWB while assuring that the clips stay on the PWB and fully function to discharge any static electrical charge on the peripheral card cover parts to the grounding sockets in the peripheral card, provide a means for electro-magnetic shielding by grounding the conductive case, and provide a wiping action which tends to break through any oxide or contamination layer between the clip and the conductive surface of the case.